ITT: religious nuts.
Marriage won't make your relationship one bit better (unless you are both religious nuts). There is no higher degree of commitment between married and unmarried couples. Your relationship will fall apart just the same either way if you two are not compatible. If you both want to get married, great, happy for you. This doesn't change the fact that there is no moral reason to do so and oftentimes marriage is financially irresponsible. If you love someone, are you going to leave just because they aren't married? If you two become incompatible for whatever reasons, think just being married is going to keep your partner around?
There are all kinds of things you need to see BEFORE getting married, even after discussing them, as any discussion is likely to include an idealized version of your so's life (ie I always do the dishes right away, I clean 3 times a week, my dog almost never barks, etc.).
Anyways, some basic things to discuss include:
1. finances
2. cooking/eating out
3. division of chores/work around the house
4. pets
5. children
6. where you want the relationship to go long term (if you want marriage or kids)
7. work hours
8. alarm clock
9. hobbies/exercise/running
10. having guests over/family visiting
In most of the best relationships I've seen the couples were already living together before they got married or have even elected not to get married ever. Some of the worst relationships I've seen were people who got married young, after only dating for a year or two in or shortly after college. People change significantly in their mid to late 20s when they start working. They stop being cool, stop working out; they replace all this with 60+ hours a week of work. Or maybe they don't change at all. They never stop drinking 5 beers a night, only now instead of a partying college kid they're just an alcoholic actuary.
If you're not living together you're only seeing your partner at his or her best. You need to know you can love them the rest of the time before you consider marriage.